The disclosures of Japanese Patent Applications Nos. 2001-135026 filed on May 2, 2001 and 2001-226436 filed on Jul. 26, 2001, including their specifications, drawings and abstracts, are incorporated herein by reference in their entireties.
1. Field of Invention
The invention relates to a fuel vapor handling apparatus of an internal combustion engine, and to a diagnostic apparatus of the fuel vapor handling apparatus.
2. Description of Related Art
Internal combustion engines that use a high-volatile fuel, such as gasoline or the like, are equipped with a fuel vapor handling apparatus for preventing fuel vapor formed in a fuel tank from being released into the atmosphere. Fuel vapor handling apparatus equipped with a canister are widely known. A canister is formed by a container and a fuel adsorption-capable adsorbent contained in the container. Fuel vapor introduced from the fuel tank via a fuel vapor introducing port is temporarily adsorbed to the adsorbent. If negative pressure is caused in an intake pipe due to operation of the internal combustion engine, atmospheric air is supplied into the canister via an atmospheric port due to the negative pressure, so that fuel desorbs from the adsorbent, and is purged into the intake pipe via a purge port. The purged fuel is drawn into engine cylinders together with intake air, thus forming a portion of the air-fuel mixture.
In direct injection type internal combustion engines that conduct stratified charge combustion, or internal combustion engines installed in hybrid vehicles that use an electric motor and an internal combustion engine as drive power sources, the degree of opening of a throttle valve is set to a value relatively shifted to a fully-open side, and therefore there may be a case where the negative pressure used to purge the fuel vapor adsorbed to the canister lacks. Hence, the fuel vapor purge capability is reduced. A technology is proposed (for example, in Japanese Patent Application Laid-Open No. 5-340315) which makes up for insufficient negative pressure in the intake pipe by providing a purge pump on an atmospheric port side or on a purge port side, and increasing the pressure at the side of the atmospheric port of the canister or increasing the negative pressure at the side of the purge port so as to accelerate the supply of air into the canister.
Another technology that adjusts the amount of purge by changing the strength of rotation of a purge pump is proposed in Japanese Patent Application Laid-Open No. 11-30185.
However, the aforementioned technologies described in Japanese Patent Application Laid-Open Nos. 5-340315 and 11-30185 are not necessarily practical if accessory loss and the life spans of the purge pump and its power output section are taken into consideration.
It is one object of the invention to provide a practical fuel vapor handling apparatus having a purge pump.
In accordance with a first aspect of the invention, a fuel vapor handling apparatus includes a fuel vapor introducing port connected to a fuel tank, a purge port connected to an intake pipe of an internal combustion engine, and a canister which is formed by a container containing an adsorbent that adsorbs a fuel vapor from the fuel tank, and which has an atmospheric port that is open to an atmospheric pressure. The apparatus supplies air into the canister via the atmospheric port by using a purge pump, and purges a fuel desorbed from the adsorbent into the intake pipe via the purge port. The fuel vapor handling apparatus further includes a controller that controls the purge pump. The controller is set so that the purge pump intermittently operates.
Due to the intermittent operation, the canister internal temperature, which is reduced by the latent heat of vaporization at the time of desorption of fuel during an operating period, rises due to heat transferred from a canister-installed atmosphere and the like during a non-operating period between operating periods. Thus, desorption of fuel is facilitated. Therefore, fuel can be purged efficiently. Furthermore, corresponding to the amount of non-operating periods, the actual operating time of the purge pump is reduced, and the life of the purge pump increases. Practicality thus improves.
In the first aspect described above, the fuel vapor handling apparatus may further include a heater that heats an interior of the canister.
Therefore, during a non-operating period, the canister internal temperature can be sufficiently recovered from a temperature level to which it was reduced during the operating period. Hence, the purging can be more efficiently performed. Corresponding to an enhanced recovery from a reduced canister internal temperature, the load on the purge pump is reduced. Therefore, a low-output purge pump will suffice, and the life of the purge pump can be further increased.
In the first aspect, the controller may control a purge valve that changes between a connection between the canister and the intake pipe and a disconnection between the canister and the intake pipe, as well as the purge pump. In addition, the controller may be set so that the purge pump and the purge valve intermittently operate, and so that a timing at which the purge valve opens is delayed a predetermined time from a timing at which the purge pump turns on.
Since the timing at which the purge valve opens is delayed from the timing at which the purge pump turns on, a period during which the amount of flow of air becomes unstable due to a delay in starting the purge pump is excluded from the actual purge period. Therefore, the linearity of the amount of purge flow relative to the length of the open period of the purge valve improves. Hence, the amount of purge can be precisely controlled.
In the first aspect, the controller may control a purge valve that changes between a connection between the canister and the intake pipe and a disconnection between the canister and the intake pipe, as well as the purge pump. In addition, the controller may be set so that the purge pump and the purge valve intermittently operate, and so that a timing at which the purge valve closes and a timing at which the purge pump turns off are substantially synchronous.
Since the purge valve closes substantially simultaneously with the turning off of the purge pump, a period following the turning off of the purge pump during which the amount of flow of air ejected gradually decreases and does not become constant is excluded from the actual purge period. Therefore, the linearity of the amount of purge flow relative to the length of the open period of the purge valve improves. Hence, the amount of purge can be precisely controlled.
In the above-described aspect, the controller may be set so that a timing at which the purge valve closes and a timing at which the purge pump turns off are substantially synchronous.
In addition to the exclusion of the period during which the amount of flow of air becomes unstable due to a delay in starting the purge pump from the actual purge period, the purge valve closes substantially simultaneously with the turning off of the purge pump, so that the period following the turning off of the purge pump during which the amount of flow of air ejected gradually decreases and does not become constant is also excluded from the actual purge period. Therefore, the linearity of the amount of purge flow relative to the length of the open period of the purge valve improves. Hence, the amount of purge can be precisely controlled.
In the first aspect, the controller is set so as to determine a number of on/off repetitions of the purge pump so that a cumulative amount of actual operating durations during an intermittent operation increases as an instructed purge amount increases.
If the cumulative amount of actual operating durations is prescribed in accordance with the instructed purge amount so as to use the purge pump in a restricted manner, the life of the purge pump can be increased. If a heater is provided, the cumulative amount of actual operating durations can be further reduced due to the desorption accelerating effect of the heater. Therefore, the substantial life of the purge pump can be increased. It also becomes possible to adopt a simple brush motor or the like as a power source of the purge pump.
In the first aspect, the fuel vapor handling apparatus may further include a fuel vapor concentration sensor that is provided in an intermediate portion of a passage extending from the purge port to the intake pipe and that detects a concentration of the fuel vapor. The controller is set so as to stop operating the purge pump if the concentration of the fuel vapor reaches a pre-set purge completing concentration.
Therefore, since the concentration of fuel vapor is successively monitored, it becomes possible to avoid an event in which the purge pump operates with a low purge efficiency caused by a reduced concentration of fuel vapor. Hence, the life of the purge pump can be increased. Furthermore, it becomes possible to properly set a purge period regardless of the property of fuel, or environmental factors, such as the ambient temperature and the like.
In the first aspect, the fuel vapor handling apparatus further includes a purge flow adjustor that adjusts an amount of flow of a purge toward the intake pipe, and a fuel vapor concentration sensor that is provided in an intermediate portion of a passage extending from the purge port to the intake pipe and that detects a concentration of the fuel vapor. The controller may be set so as to compute an amount of purged fuel based on the amount of flow of the purge caused by the purge pump and a result of detection by the fuel vapor concentration sensor, and so as to determine the amount of flow of the purge so that the amount of purged fuel becomes within a pre-set range. The purge flow adjustor may adjust the drive voltage of the purge pump, the duty of the purge valve, or the degree of opening of a metering valve provided at an ejection side or a suction side of the purge pump.
Therefore, a constant amount of purged fuel can always be caused to flow into the intake pipe.
In the above-described aspect, the fuel vapor handling apparatus may further include a heater that heats an interior of the canister. The controller controls the heater and the purge pump, and is set so as to start operating the heater if the amount of purged fuel is not brought into the predetermined range by an operation of the purge pump while the heater is in a non-operation state.
If the amount of purged fuel is small, the purge pump is operated at a maximum capability. If the amount of purged fuel is still less than the lower limit of the predetermined range, operation of the heater is started. By operating the heater in such a restricted manner, the electric power consumption can be reduced.
In the above-described aspect, the fuel vapor handling apparatus may further include a remaining fuel sensor that detects an amount of fuel remaining in the fuel tank. The controller is set so as to stop operating the heater if the amount of fuel remaining becomes less than a pre-set lower limit amount.
For example, if the lower limit amount is set slightly greater than a remaining amount at which refueling is required, a state where the internal temperature of the canister, that is, the temperature of the adsorbent, has decreased and good adsorption performance is possible can be obtained at the time of refueling during which fuel vapor is likely to be produced.
In the above-described aspect, the fuel vapor handling apparatus may further include a fuel vapor concentration sensor that is provided within a passage extending from the purge port to the intake pipe and that detects a concentration of the fuel vapor. The controller is set so as to stop operating the heater if the concentration of the fuel vapor becomes lower than a pre-set lower limit concentration.
If the concentration of fuel vapor is lower than the lower limit concentration, it is considered that the amount of fuel adsorbed to the adsorbent in the canister is small, and the operation of the heater is stopped. Therefore, the electric power consumption is reduced, and the loss of power available for accessories can be reduced.
In the above-described aspect, the fuel vapor handling apparatus may further include a tank internal pressure sensor that detects an internal pressure of the fuel tank. The controller is set so as to stop operating the heater if the internal pressure of the fuel tank becomes lower than a pre-set lower limit pressure.
If the fuel tank internal pressure is lower than the lower limit pressure, it is considered that the inflow of fuel vapor from the fuel tank to the canister is small, an the operation of the heater is stopped. Therefore, the electric power consumption is reduced, and the loss of power available for accessories can be reduced.
In accordance with a second aspect of the invention, a fuel vapor handling apparatus includes a fuel vapor introducing port connected to a fuel tank, a purge port connected to an intake pipe of an internal combustion engine, and a canister which is formed by a container containing an adsorbent that adsorbs a fuel vapor from the fuel tank, and which has an atmospheric port that is open to an atmospheric pressure. Using a purge pump, the fuel vapor handling apparatus supplies air into the canister via the atmospheric port, and purges a fuel desorbed from the adsorbent into the intake pipe via the purge port. The apparatus further includes a metering valve whose degree of opening is variable and which adjusts an amount of flow of the purge pump, and a controller that controls the metering valve and adjusts the degree of opening of the metering valve.
Therefore, the amount of purge can be adjusted in accordance with the degree of opening of the metering valve. Since the amount of ejection flow of the purge pump is adjusted by the metering valve, there is no need to provide a construction for adjusting the magnitude of power generated by a power unit of the purge pump, for example, a circuit for adjusting the amount of electricity supplied to the motor, that is, a power unit. Therefore, the construction is simplified, and practicality improves.
In accordance with a third aspect of the invention, a fuel vapor handling apparatus includes a fuel vapor introducing port connected to a fuel tank, a purge port connected to an intake pipe of an internal combustion engine, and a canister which is formed by a container containing an adsorbent that adsorbs a fuel vapor from the fuel tank, and which has an atmospheric port that is open to an atmospheric pressure. Using a purge pump, the fuel vapor handling apparatus supplies air into the canister via the atmospheric port, and purges a fuel desorbed from the adsorbent into the intake pipe via the purge port. The apparatus further includes a heater that heats an interior of the canister, and a controller that controls the purge pump and the heater. The controller is set so as to operate the heater before starting operating the purge pump.
Since before a purge, the temperature in the canister is raised so as to facilitate desorption of fuel from the adsorbent, the purge can be efficiently performed. Furthermore, the load on the purge pump is reduced. Therefore, a low-output purge pump suffices, and the life of the purge pump can be increased. Thus, practicality improves.
In accordance with a fourth aspect of the invention, a fuel vapor handling apparatus includes a fuel vapor introducing port connected to a fuel tank, a purge port connected to an intake pipe of an internal combustion engine, and a canister which is formed by a container containing an adsorbent that adsorbs a fuel vapor from the fuel tank, and which has an atmospheric port that is open to an atmospheric pressure. Using a purge pump, the fuel vapor handling apparatus supplies air into the canister via the atmospheric port, and purges a fuel desorbed from the adsorbent into the intake pipe via the purge port. The apparatus further includes a controller that controls the purge pump, and a refueling detecting sensor that detects whether the fuel tank has been refueled. The controller is set so that the purge pump starts operating when refueling is performed.
Since refueling causes production of a great amount of fuel vapor, performing a purge following refueling achieves good purging efficiency. Since the purge pump stops operating at the elapse of a predetermined period, the life of the purge pump can be increased. Thus, practicality improves.
Since the stop timing of the purge pump (i.e., the timing at which the purge pump is stopped) is prescribed by the concentration of fuel vapor, it becomes possible to properly set a purge period regardless of the property of fuel, or environmental factors, such as the ambient temperature and the like.
In accordance with a fifth aspect of the invention, a fuel vapor handling apparatus includes a fuel vapor introducing port connected to a fuel tank, a purge port connected to an intake pipe of an internal combustion engine, and a canister which is formed by a container containing an adsorbent that adsorbs a fuel vapor from the fuel tank, and which has an atmospheric port that is open to an atmospheric pressure. Using a purge pump, the fuel vapor handling apparatus supplies air into the canister via the atmospheric port, and purges a fuel desorbed from the adsorbent into the intake pipe via the purge port. The apparatus further includes a controller that controls the purge pump, and a fuel vapor concentration sensor that is provided within a passage extending from the purge port to the intake pipe, and that detects a concentration of the fuel vapor. The controller is set so that the purge pump starts operating if the concentration of the fuel vapor exceeds a pre-set concentration.
Since a purge is performed when a great amount of fuel vapor is produced, the purge can be efficiently performed, and the life of the purge pump can be increased. Thus, practicality improves.
In accordance with a sixth aspect of the invention, a fuel vapor handling apparatus includes a fuel vapor introducing port connected to a fuel tank, a purge port connected to an intake pipe of an internal combustion engine, and a canister which is formed by a container containing an adsorbent that adsorbs a fuel vapor from the fuel tank, and which has an atmospheric port that is open to an atmospheric pressure. Using a purge pump, the fuel vapor handling apparatus supplies air into the canister via the atmospheric port, and purges a fuel desorbed from the adsorbent into the intake pipe via the purge port. The apparatus further includes a controller that controls the purge pump, and a fuel vapor concentration sensor that is provided within a passage extending from the purge port to the intake pipe and that detects a concentration of the fuel vapor. The controller is set so as to compute an amount of purged fuel based on the amount of flow of a purge and a result of detection by the fuel vapor concentration sensor, and is set so that the purge pump operates if the concentration of the fuel vapor exceeds a pre-set concentration.
Since a purge is performed when a great amount of fuel vapor is produced, the purge can be efficiently performed, and the life of the purge pump can be increased. Thus, practicality improves.
In accordance with a seventh aspect of the invention, a fuel vapor handling apparatus includes a fuel vapor introducing port connected to a fuel tank, a purge port connected to an intake pipe of an internal combustion engine, and a canister which is formed by a container containing an adsorbent that adsorbs a fuel vapor from the fuel tank, and which has an atmospheric port that is open to an atmospheric pressure. Using a purge pump, the fuel vapor handling apparatus supplies air into the canister via the atmospheric port, and purges a fuel desorbed from the adsorbent into the intake pipe via the purge port. In this apparatus, the purge pump is of a circumferential flow type in which an impellor rotatably disposed in a pump housing is driven by a motor connected to an end of a shaft of the impellor so as to transfer a rotational energy of the impellor to the air sucked via a suction opening and moving through the pump housing to an ejection opening. A connecting portion between the impellor and a rotating shaft of the motor has a structure in which the impellor and the rotating shaft are slidable in a thrust direction, and in which contact surfaces of the impellor and the rotating shaft of the motor have a slip stopper portion that is oblique to a direction of a circumference about the rotating shaft of the motor, and in which a gap is formed between a surface of the impellor and a surface of the rotating shaft of the motor that face each other in the thrust direction.
The impellor has a play in the direction of thrust with respect to the motor rotating shaft, within the range of the gap. Therefore, even if the motor deviates in position in the direction of thrust, interference between the impellor and the housing is avoided. Therefore, no overload occurs on the motor, and the purge can be efficiently performed. Furthermore, the life of the purge pump can be increased. Thus, practicality improves.
In the above-described aspect, bearings of the impellor may be provided on opposite sides of a body portion of the impellor.
Since the impellor is journaled at two end sides, the axis of the impellor does not incline, and interference between the impellor and the housing is avoided. Therefore, avoidance of overload on the motor is further ensured.
In an eighth aspect of the invention, a diagnostic apparatus for detecting an operation abnormality of the fuel vapor handling apparatus described above as any one of the first to seventh aspects includes an actuator, a pressure sensor and a controller. The controller controls a purge valve that changes a connection between a canister and an intake pipe and a disconnection between the canister and the intake pipe. The pressure sensor detects a pressure in a closed space that is formed upon the disconnection from the intake pipe caused by the purge valve, and that includes the canister and a fuel tank, and which outputs a detection signal to the controller. The controller pressurizes the closed space by operating the purge pump while the purge valve is closed, and determines an operation state of the purge pump based on an increasing rate of the pressure detected by the pressure sensor.
If the purge pump is normal, the pressure in the closed space is increased at a predetermined increasing rate by operation of the purge pump. However, if the purge pump is abnormal and its air ejecting capability drops, the pressure increasing rate becomes less the normal rate. Therefore, it becomes possible to determine a state of operation of the purge pump based on the pressure increasing rate.
In the above-described aspect, the controller may be set so as to compare the pressure detected by the pressure sensor with a target pressure, and compare a time of operation of the purge pump during a closed state of the purge valve with a pre-set upper limit time. Furthermore, the controller may be set so as determine that the purge pump has an operation abnormality if the time of operation of the purge pump becomes longer than the upper limit time while the detected pressure is below the target pressure.
A reduction in the increasing rate of the pressure in the closed space prolongs the time needed before the target pressure is reached. Therefore, if the operating time of the purge pump with the purge valve closed becomes longer than the upper limit time, it can be determined that the purge pump has an operation abnormality.
In a ninth aspect of the invention, a canister purge system includes a canister that adsorbs a fuel vapor from a fuel tank of an internal combustion engine, a vapor passage that connects a space formed above a fuel liquid surface in the fuel tank to the canister, a purge passage that connects the canister and an engine intake passage, an atmospheric port that places the canister and an atmosphere in communication, a purge pump that supplies a gas from the intake passage to the canister via the purge passage, and that is operable independently of an operation of the engine, and purge pump controller that supplies the fuel vapor remaining in the engine intake passage into the canister by operating the purge pump after the engine stops.
That is, the purge pump is provided for supplying fuel vapor residing in the engine intake passage to the canister. The purge pump is driven by a drive power source, such as an electric motor or the like, which is operable independently of operation of the engine. Therefore, the purge pump can be operated even after the engine stops. Hence, fuel vapor produced in the intake passage after a stoppage of the engine is delivered to the canister by operating the purge pump, so that fuel vapor adsorbs to the adsorbent in the canister. Therefore, release of fuel vapor from the intake passage after the engine stops can be prevented.
In the ninth aspect of the invention, the purge pump may be a reversible pump, and the purge pump controller may operate the purge pump in a forward direction so as to supply the fuel vapor from the canister to the engine intake passage via the purge passage during an operation of the engine, and the purge pump controller may operate the purge pump in a reverse direction to supply the fuel vapor remaining in the engine intake passage into the canister after the engine stops.
In this construction, the purge pump is a pump capable of forward operation and reverse operation. If the purge pump is operated forward during an operation of the engine, the direction of flow of gas that passes through the pump becomes such a direction as to cause fuel vapor from the canister to the intake passage, so that the purging of the canister is performed. If the purge pump is reversely operated after the engine stops, gas moved through the pump flows in such a direction from the intake passage toward the canister, so that fuel vapor residing in the intake passage is adsorbed by the canister. Therefore, using a single purge pump, atmospheric discharge of fuel vapor can be prevented during operation of the engine and after the engine stops.
In the ninth aspect, the purge pump may be disposed in the purge passage.
In this construction, therefore, the purge pump is disposed on the purge passage connecting the intake passage and the canister. In this case, during forward operation of the pump, fuel vapor in the canister is delivered into the intake passage via the pump provided in the purge passage. During reverse operation of the pump, fuel vapor in the intake passage flows through the pump in the reverse direction, and is delivered to the canister.
In the ninth aspect, the purge pump may be connected to the atmospheric port of the canister.
In this construction, the purge pump is connected to the atmospheric port of the canister. In this case, during forward operation of the pump, the pump delivers atmospheric air into the canister, and desorbs fuel vapor adsorbed to the canister, so that a mixture of fuel and air flows into the intake passage via the purge passage. If the pump is reversely operated, air from which fuel vapor has been removed by the canister is drawn from the canister, so that negative pressure occurs in the canister. Therefore, fuel vapor remaining in the intake passage flows into the canister via the purge passage.
In the ninth aspect, the purge pump controller may suspend an operation of the purge pump if an engine temperature after the engine stops is at most a predetermined temperature.
Therefore, if the engine temperature after a stoppage of the engine is lower than or equal to the predetermined temperature, operation of the purge pump is suspended. If the engine temperature is low, the temperature of an intake passage wall surface is correspondingly low. Therefore, if the engine temperature is low, the vapor pressure of fuel in the intake passage is also low, so that fuel remaining in the intake passage becomes less likely to vaporize. During this state, substantially no fuel vapor is released from the intake passage to the outside. Therefore, even if the purge pump is stopped, atmospheric discharge of fuel vapor does not occur. Hence, according to the invention, if the engine temperature has dropped to a level that allows substantially no atmospheric discharge of fuel vapor, the pump drive energy can be reduced by stopping the purge pump.
The engine temperature can be detected by, for example, directly measuring the temperature of an intake passage wall surface. It is also possible to detect at least one of the cooling water temperature, the intake air temperature, the intake air temperature in the intake passage, etc. and to use them as parameters that indicate the engine temperature.
In the ninth aspect, the purge pump controller may continue operating the purge pump for a predetermined operation time after the engine stops, and then stop operating the purge pump. In addition, the purge pump controller may set the predetermined operation time shorter if an engine temperature after the engine stops is higher.
Therefore, the purge pump is operated only while fuel vapor is present in the intake passage. The amount of fuel vapor produced in the intake passage increases with increases in the engine temperature occurring after the engine stops. Therefore, if the engine temperature after a stoppage of the engine is high, the fuel vapor remaining in the intake passage vaporizes into fuel vapor within a relatively short time. Hence, if the purge pump is operated after a stoppage of the engine, the entire amount of fuel remaining in the intake passage is adsorbed in the form of fuel vapor by the canister in a shorter time if the engine temperature is higher. After that, no more fuel vapor is produced in the intake passage. In this invention, the purge pump is operated only for a period during which fuel vapor is produced in the intake passage. Therefore, the pump drive energy can be reduced.
In the ninth aspect, the purge pump controller may start operating the purge pump after a predetermined delay time elapses following a stoppage of the engine, and the purge pump controller may set the predetermined delay time based on an engine temperature occurring when the engine stops.
Therefore, operation of the purge pump is started at a timing at which the fuel vapor produced in the intake passage actually reaches a connecting portion between the purge passage and the intake passage. The purge pump sucks fuel vapor from the intake passage via the purge passage. However, although fuel vapor is mainly produced near an intake port of the intake passage, the connecting portion (purge opening) between the intake passage and the purge passage is remote from the intake port. Therefore, a delay time occurs before the fuel vapor produced near the intake port reaches the purge opening. This delay time becomes short if the engine temperature is high and fuel vapor is rapidly produced in a great amount after a stoppage of the engine. This delay time becomes relatively long if the engine temperature is low and the amount of fuel vapor produced is small. In this embodiment, the delay time in operating the purge pump is set based on the engine temperature occurring at the time of stoppage of the engine. Therefore, operation of the purge pump can be started at the timing at which fuel vapor actually reaches the purge opening. Hence, it becomes possible to operate the purge pump at a truly needed timing. Therefore, the energy for driving the pump can be reduced.
In the ninth aspect, if after a stoppage of the engine, there is an engine temperature rise above an engine temperature occurring at the stoppage of the engine, the purge pump controller may operate the purge pump in accordance with the engine temperature rise.
Therefore, if the engine temperature increases after a stoppage of the engine, the purge pump is reversely operated. For example, if the engine temperature at a stoppage of the engine is low, the fuel remaining in the intake port mostly remains in the intake port without vaporizing. Therefore, operation the purge pump during the stoppage of the engine will not eliminate fuel remaining in the intake port. However, if the engine temperature (intake port temperature) becomes higher than the temperature occurring at the time of the stoppage of the engine due to the effect of an air temperature rise, radiation heat of direct sunlight or the like, fuel remaining in the intake port during low temperatures may vaporize and fuel vapor may be discharged from the intake passage into the atmosphere. In the invention, in order to prevent discharge of fuel vapor due to a rise in engine temperature, the purge pump is operated in accordance with an engine temperature rise above the temperature occurring at the time of the stoppage of the engine, if there is any temperature rise. The aforementioned xe2x80x9cthe purge pump is operated in accordance with an engine temperature risexe2x80x9d includes not only starting operating the purge pump if the temperature rises by at least a certain amount, but also changing the operating duration of the pump in accordance with, for example, the size of increase in temperature, or operating the purge pump every time the engine temperature increases by a predetermined amount after the engine stops. In this aspect of the invention, since the purge pump is operated in accordance with an increase in the engine temperature after the stoppage of the engine, atmospheric discharge of fuel vapor can be reliably prevented even if the engine temperature at the time of a stoppage of the engine is low and fuel liquid remains in a relatively great amount in the intake port.
In the ninth aspect, the canister purge system may further include a diagnostic apparatus which, after a stoppage of the engine, causes the purge pump to operate in the reverse direction by using the purge pump controller, and thereby adjusts an internal pressure of a purge system that includes the purge passage, the canister and the fuel tank, to a value that provides a pressure difference relative to an atmospheric pressure, and which, after the internal pressure is adjusted, closes the purge system, and determines whether the purge system has a leak based on a change that occurs in the internal pressure of the purge system after the purge system is closed.
Therefore, a pressure difference between the purge system and the atmosphere can be caused by operating the purge pump in the reverse direction when it is to be determined whether the purge system has a leak after a stoppage of the engine. For example, when it is determined whether the purge system has a leak, the purge system internal pressure is adjusted to a positive pressure or a negative pressure that causes a pressure difference relative to the atmospheric pressure, and a change in the purge system internal pressure caused by entrance of air into the purge system via a leak or exit of gas from the system into the atmosphere via a leak is measured. In this manner a diagnostic operation is performed.
In this case, due to a diagnostic performed by causing a difference in pressure between the purge system and the atmosphere through a reverse operation of the purge pump, entrance of fuel vapor from the purge system into the intake system is prevented. For example, in a construction in which the purge pump is disposed in the purge passage, air is drawn from the intake passage, and is delivered into the canister by reversely operating the purge pump, so that the purge system has a positive pressure. In a construction in which the purge pump is connected to the atmospheric port, a negative pressure is caused in the canister by discharging air from the canister into the atmosphere. Therefore, in either one of the constructions, a flow from the intake passage toward the canister is formed when the purge pump is reversely operated. Therefore, during performance of a diagnostic operation, fuel vapor in the canister or the purge system does not enter the intake passage.